Generally, image display devices can be divided into devices for multiple persons to enjoy images displayed thereon such as televisions and projectors, and personal display devices by which displayed images are enjoyed personally such as personal computers, televisions set in the chairs in an airplane, and cell phones. In the case of the former ones, for multiple persons to appreciate images, the images are required to be displayed at a position distant from the picture plane, and thus there is the disadvantage that there arises a restriction with respect to the size of the display, and, at the time, a large space is required. On the other hand, since the latter ones are for personal use, images may be displayed near the picture plane, and even if the picture plane itself is small, the images can be observed with a field angle comparable to that of the above-described televisions or projectors. However, since focal position is located near the user, there also is a restriction concerning the field angle (the user can approach such a display only down to a distance of from 30 to 40 cm); since the focal position is located near the user, the user is apt to be tired, and, moreover, wide range images having a field of view angle of more than 30 degrees cannot be obtained from such a display.
What was devised to solve the latter problem was eyeglass type displays and head mount type displays, namely, these displays are configured such that their image display portions are attached on the head, or such that their image display portions such as eyeglass frames are attached on the face; large picture planes located at a distant focal position are viewed with virtual images. However, in order to be attached on the head, they are required to be made light, and both of their image quality and field angle are unsatisfactory. On the other hand, as a method to satisfy high performances of both of image quality and field angle, there are systems configured such that with the heavy object of an image display portion of high image quality and high field angle being fixed on a position other than a user, the user looks into the image display portion, or with the sight line position being detected, the image display device is made to follow the detected sight line position by actuators (for example, see Patent Document 1 and Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Publication Hei 5-293790.    Patent Document 2: Japanese Unexamined Patent Publication Hei 10-161058.